Sterically Demanding Diphosphonite Ligands –Synthesis and Application in Nickel‐Catalyzed Isomerization of 2‐Methyl‐3‐Butenenitrile

Abstract

Dedicated to Professor Joachim Bargon (Universit‰t Bonn) on the occasion of his 65 th birthday.Abstract: The synthesis of a novel class of sterically demanding diphosphonites 1 ± 8, based on rigid backbones, is described. The starting materials are all commercially available and the methodology allows for a modular approach. All ligands have been fully characterized, including an X-ray crystal structure for compound 1, 4,5-bis{di[(2-tert-butyl)phenyl]phosphonito}-9,9-dimethylxanthene. The coordination of these diphosphonite ligands towards Ni(II) and Ni(0) precursors is investigated, both by NMR spectroscopy as well as X-ray crystallography and compared with the behaviour of diphosphine ligands such as Xantphos. The molecular structure for complex 9, trans-[NiBr 2 (1)] is described in detail. The nickel-catalyzed isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile is studied, a relevant step in the industrially important hydrocyanation of butadiene (the DuPont adiponitrile process). Good activities and selectivities to the desired 3-pentenenitrile are obtained in this reversible C À C bond activation reaction.

Phosphonite Ligand Design for Nickel‐Catalyzed 2‐Methyl‐3‐butenenitrile Isomerization and Styrene Hydrocyanation

“…We attribute this to the known tendency of chelating phosphonite ligands to form very stable tetrahedral bis‐chelate complexes with nickel(0), as has been reported by Vogt et al. for their phosphonite derivatives of Xantphos 10g…”

“…Most remarkably, the reaction proceeded with excellent selectivity, yielding exclusively t 3PN as a product, even when heating the reaction mixture for 20 h. In terms of activity, 15 is, to our knowledge, superior to any other phosphonite described for this reaction and is very similar in activity to the phosphites patented by Du Pont. Table 1 summarizes known activity data for 2M3BN– t 3PN isomerizations with phosphonites ( 20 is from our own group [11] , 23 and 24 represent the most active phosphonites based on the xanthene backbone developed by Vogt et al 10g16).…”

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

“…To probe route i we set out to synthesize [(TBBP)AlOH] by controlled hydrolysis of an alkyl precursor. Although the synthesis and structure of monomeric [(TBBP)AlMe ⋅ THF] is known, we attempted the synthesis of the THF‐free precursor [(TBBP)AlMe] by reacting (TBBP)H 2 with Me 3 Al. The stoichiometric reaction led to a poorly defined mixture of products, whereas excess Me 3 Al gave the [(TBBP)AlMe ⋅ AlMe 3 ] adduct from which coordinated Me 3 Al could not be removed.…”

“…The solvents were dried on alumina columns and were degassed by bubbling nitrogen through the solvent reservoir. t Bu 3 Al, (TBBP)H 2 , (TBBP)AlMe ⋅ THF, (DIPPnacnac)AlMe−O−Zr(Me)Cp 2 , and MAO were prepared according to reported literature procedures. Me 3 Al (97 %) and i Bu 3 Al were purchased from Sigma Aldrich, and [PhMe 2 NH] + [B(C 6 F 5 ) 4 ] − was purchased from Boulder Scientific; all these reagents were used as received, except i Bu 3 Al which was distilled prior to use.…”

Nickel(0)-Catalyzed Equilibrium Reaction of 3-Pentenenitrile

“…在已报道的有 关 2-甲基-3-丁烯腈(2M3BN)异构化为 3-戊烯腈(3PN) 的文献中, 零价镍催化体系主要是由环辛二烯镍和含磷 配体组成, 含磷配体主要包括膦 [9,10] 、单烷氧基膦 [11] 、 磷酸酯 [12] 和亚磷酸酯 [13] 等.近来出现该反应在水溶液 [14] 和离子液体 [15] 中进行的报道. 所有关于 2M3BN 异构为 3PN 的零价镍催化的反应过程中, 都产生了中间体 π-烯 丙基镍化合物 [16] .…”